Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 71. Synthesis of tungsten–iridium complexes. Crystal structures of [W2Ir(µ3-RC2R)Cl(CO)4(η-C5H5)2]·CH2Cl2 and [W2Ir(µ-CR)(µ3-CR)Cl(CO)4(η-C5H5)2](R = C6H4Me-4)

Abstract

In tetrahydrofuran at room temperature, the complexes [W(CR)(CO)₂(η-C₅H₅)](R = C₆H₄Me-4) and [IrCl(CO)(η-C₈H₁₄)₂](C₈H₁₄= cyclo-octene) afford a chromatographically separable mixture of five cluster compounds [W₂Ir(µ₃-RC₂R)Cl(CO)₄(η-C₅H₅)₂](1), [W₂Ir(µ-CR)(µ₃-CR)Cl(CO)₄(η-C₅H₅)₂](2, 3, and 4, isomers), and [W₂Ir₂(µ₄-RC₂R)(µ-CO)₂(CO)₆(η-C₅H₅)₂](5). The reaction between [W(CR)(CO)₂(η-C₅H₅)] and [IrCl(CO)₂(NH₂C₆H₄Me-4)] yields a similar mixture except that (2) is absent, and a possible reason for this is discussed. The molecular structures of compounds (1) and (2) have been established by single-crystal X-ray diffraction studies. That of (1) consists of a triangle of metal atoms [W–W 2.666(1), W–Ir 2.821(1) and 2.798(1)Å] with the W–W bond weakly semi-bridged by a CO ligand [W–C–O 169.1(9)°]. The alkyne RC₂R adopts a µ₃(η²-⊥) bonding mode, transversely bridging a W–Ir bond, and tilted so that one of the ligated carbon atoms triply bridges the metal triangle [µ₃-C–Ir 2.05(1), µ₃-C–W 2.24(1) and 2.28(1)Å]. The tungsten and iridium atoms of the W–Ir bond transversely bridged by the alkyne are, respectively, co-ordinated by Cl and C₅H₅, and by two CO groups. The other tungsten atom, carrying the semi-bridging CO ligand, is ligated by a CO and a C₅H₅ group. Compound (2) also has a triangular core [W–W 2.951(1), W–Ir 2.867(1) and 2.698(1)Å]. One of the p-tolylmethylidyne ligands caps the metal triangle [µ₃-C–W 2.04(2) and 2.07(2), µ₃-C–Ir 2.19(2)Å] while the other bridges the shorter W–Ir edge [µ-C–W 1.90, µ-C–Ir 2.06(2)Å]. The tungsten atom of this edge carries a CO group and a C₅H₅ moiety. The other tungsten atom is ligated by Cl, CO, and C₅H₅ groups. Two CO ligands are co-ordinated to the iridium. The molecular structures of the isomers of (2), compounds (3) and (4), have been assigned from consideration of their n.m.r. spectra (¹H and ¹³C-{¹H}) and by comparison with those of complex (2) and a PPh₃ derivative [W₂Ir(µ-CR)(µ₃-CR)Cl(CO)₃(PPh₃)(η-C₅H₅)₂] of (4) shown to contain an Ir(CO)(PPh₃) group. Like (2), complexes (3) and (4) have µ-CR, µ₃-CR, and terminal W–Cl groups. However, in (3) the µ-CR ligand bridges a W–W bond and there is an Ir(CO)₃ group present, whereas (4) is structurally very similar to (2) differing only in the site of the terminal Cl atom and a CO group. The spectroscopic data (i.r. and ¹H and ¹³C-{¹H} n.m.r.) for the tetranuclear cluster (5) are discussed and its structure can be assigned on the basis of an earlier synthesis.